1. Field of the Invention
The present invention relates to a thin-film piezoelectric device used for fine positioning by inverse piezoelectric effect of piezoelectric layer, a production method thereof, and a head gimbals assembly using the thin-film piezoelectric device and, more particularly, to a positioning structure for a magnetic head which performs reading and writing of recording information in a magnetic recording disk device.
2. Related Background Art
The recent approach toward higher density and larger capacity of magnetic recording (hard disk) increases the necessity for a thin-film piezoelectric device as a high-accuracy positioning mechanism of tracking. For example, Patent Literatures 1-3 below disclose the thin-film piezoelectric devices of this kind.
Patent Literature 1 (Japanese Patent Application Laid-open No. 2005-286037) discloses the thin-film piezoelectric device in which a piezoelectric laminate 21A wherein a piezoelectric layer 16A is interposed between a pair of electrode layers 14A, 18A and a piezoelectric laminate 21B wherein a piezoelectric layer 16B is interposed between a pair of electrode layers 14B, 18B are superimposed through an adhesive layer 12. Patent Literature 2 (Japanese Patent Application Laid-open No. 2002-34807) discloses the thin-film piezoelectric device composed of a pair of thin-film piezoelectric devices 10A and 10B in a double-layer structure of first thin-film piezoelectric 11A and second thin-film piezoelectric 11B electrically short-circuited through an electroconductive adhesive 13. Patent Literature 3 (Japanese Patent Application Laid-open No. 2003-101095) discloses the thin-film piezoelectric device in which a structure 66 is formed in a configuration wherein a first piezoelectric thin layer 53 sandwiched between first lower electrode layer 52 and first upper electrode layer 54 and a second piezoelectric thin layer 57 sandwiched between second lower electrode layer 56 and second upper electrode layer 58 are bonded through an adhesive layer 60, and in which an insulating layer 62 is formed so as to cover the structure 66.
However, all the thin-film piezoelectric devices disclosed in Patent Literatures 1-3 have the two piezoelectric laminates including the respective piezoelectric layers and this configuration makes it difficult to satisfy the market demands of mass productivity and low price. The reason why the presently existing thin-film piezoelectric devices adopt this double-layered piezoelectric laminate structure, is that the thin-film piezoelectric devices are comprised of thin layers. Specifically, during a process of depositing layers including the piezoelectric layer on a substrate, the substrate is warped by various stresses due to heat, lattice constant mismatch, etc. and thus the thin-film piezoelectric device obtained through the production process is also largely warped. The warpage will cause displacement in a direction different from an aimed direction of the piezoelectric laminate in the thin-film piezoelectric device (which will be referred to hereinafter as flexural displacement). When the conventional thin-film piezoelectric device with the two piezoelectric laminates is operated, the displacement directions of the two piezoelectric laminates are matched to suppress the flexural displacement so as to achieve displacement in the longitudinal direction as aimed; therefore, the piezoelectric device has to be constructed in the laminated structure of the two piezoelectric laminates. For this reason, a single-layered piezoelectric laminate structure failed to achieve higher performance and higher reliability of the thin-film piezoelectric device and an apparatus incorporating the thin-film piezoelectric device of this structure inevitably suffered breakage, trouble, and so on.
Because of the above problem, the double-layered piezoelectric laminate structure consisting of the two layers of piezoelectric laminates bonded was adopted to cancel the warpage during production and during operation, thereby suppressing deformation of the device and suppressing the flexural displacement.
The present invention has been accomplished in light of the above-described problem and an object of the present invention is to provide a thin-film piezoelectric device capable of achieving higher performance, higher reliability, and lower cost by a single-layer piezoelectric laminate, a production method thereof, and a head gimbals assembly and a hard disk drive using the thin-film piezoelectric device.